The present invention relates to integrated circuits, and more particularly, to debonding integrated circuits.
Integrated circuits are formed from semiconductor wafers. In a typical semiconductor fabrication process, numerous integrated circuits are formed on a silicon wafer. To facilitate operations such as via formation for backside ball grid arrays, it is often desirable to thin a silicon wafer. Because silicon wafers can become fragile when thinned, wafers are bonded to a carrier before thinning. The carrier helps to stabilize the silicon wafer and prevents the wafer from cracking during thinning and handling during subsequent processes.
During wafer thinning, the backside of the silicon wafer is ground down using a series of grinding and polishing steps. The final silicon wafer thickness may be on the order of 5 to 100 μm. Following wafer thinning, backside processing operations may be performed such as via formation, solder bump formation, and laser annealing.
Once backside processing is complete, a wafer debonding tool is used to separate the thinned silicon wafer from the carrier. The wafer debonding tool contains two heated vacuum chucks. An upper vacuum chuck holds the backside of the silicon wafer while a lower vacuum chuck holds the carrier. A shearing motion is used to pull the silicon wafer from the carrier. Other types of wafer debonding scheme are also sometimes used. These wafer debonding schemes may be based on perforated carrier arrangements, laser debonding configurations, thermal release debonding schemes (e.g., using an oven or hotplate), etc.
Once debonded from the carrier, the thinned wafer may be cleaned and mounted on a film frame wafer carrier. A film frame wafer carrier has a ring of metal that holds an adhesive membrane. The cleaned wafer may be placed face up in the center of the membrane for transport. Once at its intended destination, an ultraviolet light source may be used to degrade the adhesive qualities of the membrane, thereby allowing the silicon wafer to be removed. The silicon wafer can then be diced into individual die and each die may be mounted in a respective package. Dicing operations may also be performed before transport of the wafer.
These schemes pose challenges. For example, a wafer debonding tool may damage a silicon wafer. This is because any chips that form on the edge of the wafer during shear debonding have the potential to scrape across the entire wafer surface. Additionally, handling an unsupported thin wafer though the process of cleaning and film frame mounting after debond operations risks breaking the wafer.
Wafers are typically mounted face up on film frames to reduce the risk of damage from chipping caused by blade vibration during dicing operations. However, wafers that are mounted face up may become contaminated by particles. Although the impact of contamination can be mitigated somewhat by covering the wafer with a permanent glass cover that facilitates cleaning to remove contaminants, glass covers can adversely affect device performance. For example, in integrated circuit image sensors, the presence of the cover glass absorbs and reflects light. The cover glass also may distort incoming light. These optical effects tend to degrade image quality. Wafers can be mounted face down on film frames, but this poses a risk of contamination from the adhesive of the film.